1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of forming a capacitor of the semiconductor device.
2. Description of the Related Art
With an advance being made in miniaturization of a semiconductor device, there has since arisen a need for further reducing a capacitor area and so forth. A tantalum oxide film (hereinafter referred to as a Ta2O5 film) having a high permittivity has recently attracted attention as a dielectric film of a capacitor. The dielectric film needs to be rendered thin for the capacitor to have a sufficient capacitance. However, if the dielectric film is formed too thin, this will cause occurrence of leakage current therefrom. Deficiency of oxygen within the Ta2O5 film, residual impurity carbon therein, reduction of the Ta2O5 film due to oxygen being drawn into an electrode material, and so forth are regarded as causes for occurrence of leakage current from the Ta2O5 film. The technique for performing oxygen annealing after formation of the Ta2O5 film as a method of making up for deficiency of oxygen therein has been disclosed in Japanese Patent Laid-Open H 9-121035, and Japanese Patent Laid-Open H 4-199828. And a method of preventing oxygen from being drawn into an electrode material by forming the electrode material of a metal having a free energy greater than that for the Ta2O5 film has been disclosed in Japanese Patent Publication H 6-82782.
However, with the technique for performing the oxygen annealing after formation of the Ta2O5 film as disclosed in the technical literature described above, difficulty has been encountered in supplying oxygen as far as the vicinity of the interface between the Ta2O5 film and an underlayer thereof. Further, in the case of changing the electrode material, there have been cases wherein the Ta2O5 film were subjected to a damage caused by a fluorine-containing gas when forming an electrode over the Ta2O5 film.
In order to solve the problems described above, a typical method of fabricating a semiconductor device according to the invention comprises steps of forming a lower electrode on the surface of a semiconductor substrate, forming a silicon nitride film over the lower electrode, applying a first heat treatment whereby the silicon nitride film is annealed in an atmosphere containing oxygen, forming a dielectric film containing alkaline earth metals over the silicon nitride film, applying a second heat treatment whereby the dielectric film is annealed in an atmosphere containing oxygen, and forming an upper electrode on the surface of the dielectric film.